Nanofluidic biosensors are defined as fluidic systems with nanometer-sized confinements and/or lateral apertures, which are used to quantify the presence of biomolecules in a solution. A majority of the current nanofluidic biosensor developments are intended for bioengineering and biotechnology applications. In the scope of this invention, biosensors are used to quantify the presence of biomolecules in solution for in vitro diagnostic applications.
Swiss patent application CH 01824/09 discloses biosensors with lateral apertures for the detection of biomolecular interactions and PCT application IB2010/050867 discloses their use with simple optical systems. The diffusion of biomolecules in these configurations are slow and require either long waiting times to attain stable measurement conditions or highly concentrated solutions for the observation of the biomolecular interactions.
Biomarkers, also called biological markers, are substances used as specific indicators for detecting the presence of biomolecules. It is a characteristic that is objectively measured and evaluated as an indicator of biological processes, pathogenic processes, or pharmacologic responses to a therapeutic intervention.
Current practices for the detection of specific biomolecules can be divided in two categories: (a) the labeled techniques and (b) the label-free techniques.
Among the labeled techniques, the widely used are fluorescence, colorimetry, radioactivity, phosphorescence, bioluminescence and chemiluminescence. Functionalized magnetic beads can also be considered as labeling techniques. Labeled techniques advantages are the sensitivity in comparison to label-free methods and the molecular recognition due to specific labeling.
Among the label-free techniques, the widely used are electrochemical biosensors, referring to amperometric, capacitive, conductometric or impedimetric sensors, which have the advantage of being rapid and inexpensive. They measure the change in electrical properties of electrode structures as biomolecules become entrapped or immobilized onto or near the electrode, but all these concepts lack molecular specific contrast, sensitivity and reliability.
Enzyme linked immunosorbent assay (ELISA) is an important biochemical technique mainly used to detect the presence of soluble biomolecules in serum, and thus is widely used as diagnostic tool in medicine and quality control check in various industries. ELISA analysis are however expensive, require large amounts of solution and is time consuming.
The other important technologies for biomolecular diagnostics are Western and Northern blots, protein electrophoresis and polymerase chain reaction (PCR). However, these methods require highly concentrated analytes and do not allow high throughput samples testing.